Microelectronic devices, such as semiconductor devices, and micro-scale mechanical, electro-mechanical, and optical devices, are generally fabricated on and/or in substrates using several different types of machines. In a typical fabrication process, an electroplating processor plates one or more layers of conductive materials, usually metals, onto a work piece, such as a semiconductor wafer or substrate. Electroplating processors generally use a contact ring having many contacts or fingers that make electrical connections to the surface of the substrate. Contact rings can be categorized into two groups: wet rings and dry rings. With a wet ring, the contact fingers are exposed to the plating bath, so that the contact fingers get “wet” during electro processing. A dry ring has a seal that seals the contact fingers, so that the contact fingers remain dry.
As semiconductor and similar micro-scale device feature sizes continue to decrease, the seed layers that can be used on wafers become thinner. This creates a high initial sheet resistance on the wafer which affects both reactor and contact fingers. In dry contact ring processors, thin seed layers are prone to inadvertent etching due to seal leaking and/or residual chemistry on the seal. Joule heating due to high currents passing through a thin seed layer can also be disruptive to uniform plating. In wet contact ring processors, a thief electrode at the edge of the wafer may be needed to control the “terminal effect” which results in a non-uniform electric field near the locations where the contact fingers touch the seed layer. However, using thief currents to control the terminal effect can deplate the seed layer around or between contact fingers, and make uniform plating problematic using wet ring processors. Thief currents also tend to cause more metal to plate onto the contact fingers.
Accordingly, engineering challenges remain in designing electroplating processors.